Sweep circuit



May 6, 1952 W. L.V GAI'NES SWEEP CIRCUIT 2 SHEETS-SHEET l Filed Deo. 24, 1949 /NVE/VTOR By W. L. GAM/E5 /Z iff/M" All A T TOR/VEV w. L. GAlNl-:s 2,595,667

SWEEP CIRCUIT 2 SHEETS-SHEET 2 May 6, 1952 Filed Dec. 24, 1949 Patented May 6, 195i rSWEEP CIRCUIT Wilbur L. Gaines, lBayside, N. Y., assignor'tofell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of-New York Application December 24, 1949, Serial No. 134,932

v8 Claims.

This invention relates `.to velectric circuits .and more specifically to .circuits for producing sweep cycles of the non-recurring type.

.Non-recurring sweep cycles vconsist basically of three .parts-'the sweeping, the restoration .and the quiescent portions. 'The sweeping .portion comprises the useful part of the cycle. -It is initiated by Ia synchronizing signal and comprises a .voltage varying unidirectionally until the peak is reached. .The restoration .portion follows and consists of the interval it takes for the sweep voltage to return from its peak vto .the normal or quiescent value. It represents the time it takes the Isweep generator vto be restored to itsnormal position ready fora new synchronizing signal. The yquiescent portion is that interval :after the sweep has been restored before a new sweeping portion has been initiated by another synchronizing signal.

The principal object of this invention is to improve the precision and vefficiency of sweep circuits of this kind.

In .precision sweep circuits, itis necessary `to insure that after one synchronizing signal has tripped the sweep generator, no further signals can affect the sweep operation until the sweep cycle is completed. Hitherto, this had been done by keeping the synchronizing amplifier inoperative only during the time the sweep generator was being actuated. In measuring high frequency disturbances `thishad the `disadvantage that -a synchronizing signal might pass during the time of sweep restoration to retrip the sweep generator before the latter had been restored to its steady or quiescent state. In accordance with .the invention, this problem is overcome by a circuit which continuously measures the .sweep voltage and keeps the .synchronizing amplifier inoperative until the sweep voltage has been restored to practically its yquiescent value. Moreover, there is a further provisionfor keeping the synchronize ing .amplifier unresponsive for an additional adjustable interval after the .sweep has been restored, so .that undesirable synchronizing pulses can be made ineffective.

Another factor important 'in high `frequency sweep circuits is the restoration time of the sweep generator. This represents a .useless part of the sweep cycle and limits the speed of response of the system, so .it is best kept at a minimum. In accordance with this invention, there is provided 'an arrangement for `-reducing this restoration time -by means of an improved changing` circuit for the sweep generator.

Another important problem 'in-the use of sweep circuits with cathode-ray tubes is .the stabilization of .the starting pointon the cathode-rayvtube screen. With most vpresent sweep circuit arrangements inwhich .direct connection is made to vthedeiiecting plates ofthe cathode-ray tube, further adjusting .is necessary, whenever fthe sweepspeed is varied, to .keep the starting ,point on :the tube screenat the .same spot. Another feature ,of the present invention is a constant potential vdivider arrangement, a specific embodiment of which is used to maintain the stability of the zero spot asthesweep speed is varied.

The invention will be more readily understood by 4referring to the following description taken in connection :with the accompanying Vc lrawings forming a part thereof in which: Y f

Fig. .1 is a block diagram showing the constituent elementsof a sweep circuit in accordance with the invention; `and Fig. 2 is a diagram of an illustrative circuit embodying the invention.

Referring more specifically to the drawings, Fig. l shows, by way of example for purposes of illustration and in block diagram form, a sweep circuit arrangement |00 in accordance with the invention. In this arrangement, a Asource of la synchronizing signal I10| supplies a sig-nail |20 to the Apreamplifier |02 which amplifies, clips and reverses when necessary to insurea positive signal. The sharpened unidirectional pulses |21 are thereafter supplied -to the control stage |03 of the synchronizing amplifier where all jbut-the lrst are cut off by the action of a control element in a manner hereinafter to be described. This one pusle is further amplified Vand reversed to produce a sharp negative pulse |22. The .pulse |22 is Athereafter used to trip the gating circuit |04 which comprises a flip-flop circuit-having vtwo positions of stability, operating andnon-operating. The output of lthe gating circuit |04 consists of a negative step pulse I| 23 which serves to control the sweep generator |05, andthe output therefrom, the sweep voltagev |24, `is applied to the sweep amplifier |06. The Yamplifier ,L06 is of the kind well known in the .art to give ,a balanced push-pull output |25 tsuitable -for-use with the deflection .plates of a cathode-ray tube.

v,Precision of control is achieved by three `separate feedback paths |01, |08 and |09. The first feedback path, the fast lock-out circuit |051. uses a portion of the gating circuit output .|23 to keep the control stage|03 of the synchronizing amplifier cut off after -`the gating circuit V|04 has been tripped. The Afirst of the `'pulses 2| supplied by -the synchronizingpreamplifier |02, after reversal and amplification by the control ,stage |03, trips the gating circuit |04 to its operating position. `A portion of thenegativestep `voltage |23 produced is supplied back to a control element of thecontrol stage |03, thereby `cutting this Vstage off and preventing all but the pulse from being ampliiied. This negativevvoltage is maintained on said control elementuntil the gating circuit |04 is restored to its nonoperating position. The second 4feedback path, the gate restoration circuit |08, lmeasures the output of the sweep generator |05 and supplies the gating circuit |04 with the pulseneeded for restoring it to its non-operating lposition when the sweep output |24 has-reached va .predetermined level. The third feedback path. the slow lock-out circuit |09, measures the sweep output |24 to keep the control stage |03 cut off until the sweep voltage |24 has been restored to its quiescent value.

Reference will now be made to Fig. 2 which is an illustrative diagram of a circuit IIE) which is part of a specic embodiment in accordance with the invention. The circuit of Fig. 2 comprises the elements indicated within the enclosure |I| of Fig. l.

'I'he sharp unidirectional pulses I2I developed by the synchronizing preamplifier |02 are supplied to the grid of control tube V4 through coupling condenser and the grid leak resistance I2. Tube V4 is operated as an amplifier. The cathode thereof is grounded, the screen grid voltage is supplied through resistances I3 and I4 from source 50, and the plate voltage is taken through resistance I4 from this same source. The suppressor grid, which serves as the aforementioned control element, is connected to the anode of tube V25 for a purpose hereinafter to be described. The anode of tube V4 is coupled to the grid of tube V1 through diode V5 which is correctly poled to pass only negative pulses. The plate voltage of tube V5 is supplied by tapping between resistances I5 and I1 which are across the source 50.

Tubes V6, V1, V8 and V9 form a, non-free running multivibrator circuit with two positions of stability, which functions as the gating circuit |04. The cathodes of tubes V6 and V9 are connected together and then through a common resistance I6 and by-pass condenser 24 to ground. The plate voltages of tubes V5, V1 and V9 are supplied through resistances I1, I8 and I9, respectively, from source 50. The grid of tube V6 is connected to the anode of tube V9 through the coupling condenser 2 I, and the anode of tube VfB is connected to the grid of the cathode follower tube V1. The cathode of tube V1 is connected through resistance 23 and the voltage-dropping gas tube V8 to the grid of tube V9. The by-pass condenser 22 is shunted across the resistance 23 and the voltage-dropping gas tube V8.

Cathode follower V22 and diode V25 make up the fast lock-out circuit |01 which consists of a feedback path from the output of the multivibrator to the suppressor grid of the control tube V4 o f the synchronizing amplier. The control grid of the tube V9 is connected to the control grid of the tube V22 through resistance 34. Tube V22 has its cathode connected through the resistance 25 to the negative terminal of the source 19. The plate voltage thereof is supplied through resistance 26 from the positive terminal of source 50 and the grid bias by tapping the common terminal between resistances 33 and 34. The other terminal of resistance 33 is connected to the negative terminal of source 10. The cathode of tube V22 is connected to the suppressor grid of tube V4 through the blocking diode V25 which is correctly poled to pass only negative pulses.

"The gating circuit output |23 also actuates the sweep generator |05. The sweep generator |05 includes tubes VI I, VI1 and VIS. The grid of the tube V9 is connected through the coupling condenser 28 to the grid of the switching tube VII. The cathode and suppressor grid of tube VII are grounded. The plate voltage of the tube VII is supplied through the variable sweep resistance 39 from the positive terminal of the source 60. The negative grid bias voltage for tube VII is supplied through resistances 3| and 33 from the negative terminal of source 10. The anode thereof is directly coupled to the grid of tube VIB. The anode of the tube VI8 is coupled directly to the grid of cathode follower tube V|1 whose cathode is connected through the variable sweep condenser 40 back to the anode of tube VI I. The cathode follower tube V|1 has its plate voltage supplied from the source 60,

Tube VI9 completes the sweep amplifier |06 and combines with the tube VIB to produce the balanced sweep output necessary for optimum cathode-ray tube operation. Tube VIS is an amplifying and inverting stage with unity gain whose output is combined with that of tube V|8 to produce a balanced push-pull sweep voltage |25. The cathodes of tube VI 8 and tube VI 9 are connected through the common cathode resistance 4| to ground. The plate voltages thereof are supplied through resistances 52 and 53, respectively, from source 89. The grid of tube VI9 is connected through resistance 51 between resistances 55 and 56 which form a voltage divider across the source 10. Condenser 58 is connected between the grid of tube VI9 and ground. The grid of tube VIS is coupled to the anode of tube VIB through resistance 6| and the associated by-pass condenser G3. There is also a feedback path through resistance 62 and its associated by-pass condenser 64 from the anode of tube VI 9 to the grid thereof. The T-network comprising resistances 6|, 62, and 51, and the condensers 63. 64, and 53 forms a feedback path from the anodes of tubes VI8 and V|9 to the grid of tube V|9 to insure unity gain therefor so that a balanced sweep output |25 is developed at the anodes of tubes V|8 and VIS. The anodes of tubes VI8 and VIS are connected, respectively, through terminals 98 and 99 to the two horizontal deiection plates of a cathoderay tube.

Tubes V29, V2| and VI 5 form the gate restoration circuit |08 which measures the magnitude of the sweep voltage and thereafter, when the proper value has been reached, generates a pulse which restores the multivibrator to its non-operating position. A measure of the sweep voltage |24 is supplied to the cathode of tube V20 through resistance 65 from the cathode of tube VI1, Resistance 66 completes the cathode circuit of tube V20 through to the negative terminal of the source 10. The grid bias of tube V29 is fixed by tapping across the potentiometer 61 which is in series with the voltage dropping gas tube VI 5 across the source 50. Condenser 68 is a high frequency shunt to ground across the resistance 61. The plate voltage of tube V20 is supplied through the resistance 1| from the source 50. The restoring pulse which is supplied to the grid of tube V6 of the multivibrator is obtained by tapping the divider, formed by the series circuit from the anode of tube V29 to the negative terminal of source 19, consisting of resistance 12, the gas tube V2I and the resistance 13, between the gas tube V2I and the resistance 13.

The slow lock-out circuit |09 comprises the tubes VIE, VI3, VI4, V24, V23 and V26. A measure of the sweep voltage |24 is supplied to the grid of tube VI6 by tapping on potentiometer 43 which is between the cathode of tube VI 1 and the negative terminal of the source 10. The cathode of tube VIB is grounded through the resistance 16. The plate voltage thereof is supplied through the resistance 11 from source 50. After amplification, the sweep voltage is fed from the plate of the tube VIE through resistance 18 to the grid of cathode follower tube VI3. Condenser 19 serves as a high frequency shunt across resistanc'e'18. "'LubeVlS derivesitsplate voltage' from sourcezll. Thegrid thereof is connected to the common terminal `of the divider formed by resistances .78 and 88. The resistance 88 is further `connected to thenegative terminal of the source 10. 'The sweep voltageis supplied from the `cathode `of tube V|3 through the voltage dropping gas -tube VM, resistance 8|, blocking diode V24 to :the grid of tube V23. Condenser 86 serves .as `a high frequency shunt across the resistance 8| vand the tube V24. vrI-'he resistance 69 is `connected to the terminal between resistance .8| and condenser 86, and the negative terminalof source 10. The cathode of l.tube Vi is also connected to the screen grid of tube VII which forms .part of the zero stabilization circuit. Tube V23 has its cathode connected through the resistance 8 2 .to the negative `terminal of the source 70, :andthe plate thereof is grounded through the Aresistance 83. VThegrid bias therefor is obtained by .connecting to the common point between resistances 84 and 8.5 which are connected ,across the source i6. The negative lock-out voltage 4developed on the plate of tube V23 is fed directly to the suppressor ,grid Vof tube V4. A prolongation of this lock-out pulse may be obtained by means of a single-shot multivibrator formed .by the addition of tube V29. The anode thereof is connected to ground, and the. grid to the common terminal of a divider formed by the resistances19| and 92 connected across the source l0. The grid thereof is further connected through the variable condenser 93 tothe anode of tube V23. The `cathode thereof Lis connected to the .cathode of tube V23.

The .operation is as follows: Suppose, for purposes of illustration. that a synchronizing signal |20 is supplied to the input of the-sweep circuit. The first of the sharp positive pulses I 2| supplied by the preamplifier to the grid of V4 is further l amplified and reversed by this last stage of the synchronizing amplifier. Thesharpened negative pulse |22 is passed through diode V5, cathode follower V1, and gas tube V9 to the grid of tube V9. Tube lV9 is that stage of the non-free running multivibrator which vis normally conducting in the non-operating position. This sharp negative pulse tends to cut tube V9 oi,

and producespa sharp positive pulse on the anode thereofwhich is transmitted by way of coupling condenser 2| to the grid of tube V6 which hitherto has beennon-conducting and tends to cause current flow to the anode of tube V5. This tendency is augmented by the negative Vdrop across cathode resistance I6 which is common to tubes V6 and V9. The two effects act cumulatively so that tube V6 quickly becomes saturated while tube V9 is cut olf. The circuit is stable in this operating position and will notreturn to its nonoperating'position until a restoring pulse is received. The cathode follower V1 is used to couple directly the plate of V6 to the grid of V9. This keeps to a minimum the input capacitance of tube V9 and insures the most rapid response. Gas tube V8 merely serves as a voltage bleeder to reduce the high cathode voltage of tube Vl to a value more suited for the grid of tube V9. The process is reversed when a negative restoring pulse is supplied to the grid of tube V6. Tube V6 tends to out olf, producing a positive pulse on the plate thereof which is transmitted through the cathode follower V7 and the gas tube V8 to the grid of tube V9, and tends to make tube V9 conducting. As before, the effect of the common cathode resistance I6 is to make the action cu- -mul'ative and tube V6 is quickly cut olf` and tube V9 .draws current.

V'Ihe negative step pulse |23 developed on the anode of tube VS when the gating circuit isprst tripped, is used to control the sweep generator |05 and also is transmitted through the tubes V22 and V25 to provide a control voltage to tube V4 of the synchronizing amplifier. This makes up what was designated the fast lock-out circuit |91. The negative pulse on-the anode of tube V6 is passed throughthe `cathode follower V1, resistance 23, gas tube V8 and resistance 34 to the grid of tube V22. Since tube V22 is used as a cathode follower, the negative pulse is continued along through the diode V25 to the suppressor grid of the tube V4. Diode V25 is l'a blocking diode and serves -toisolate the suppressor grid of the tube V4 from all but negative pulses. The negative Voltage on the suppressor grid cuts on tube V4 and makes the synchronizi-ng amplier unresponsive to further synchronizing signals while the gating circuit |94 is operated. The suppressor grid is kept at a negative potential so long as the tube V6 remains in a conducting state.

The negative pulse on tube Vt simultaneously actuates the sweep generator |05 and starts it on the sweeping portion of the sweep cycle. Tube VI is normally conducting while the gating circuit |93 is in its non-operating position. However, the sharp negative step voltage |23 produced on the anode of the tube V6 as the gating circuit is tripped, is transmitted through the cathode follower V? and the coupling condenser.

this positive voltage tends to cause an increase in the plate current of tube V|3 which decreases the voltage at the anode thereof. This negative change is returned through the cathode follower Vll' and the sweep condenser 4b to the anode of the tube VII. Hence, it may be seen that this negative feedback will tend to keep the voltage on the anode. of tube V| constant. This means that the voltage drop across sweep resistance 39 is held substantially constant so that there is a substantially constant current flow therethrough. The only path available for .this current is through the sweep condenser dil which is thus discharged by a constant current. This causes a voltage change which is linear with time across this condenser 69. Substantially all of this voltage will appear on the plate of tube VIB forming one .half of the sweep voltage. Tube V|9 is an amplifying and inverting stage with unity gain whose output is combined with that of tube V|8 to produce a balanced push-pull output |25. The sweep Voltage on the anode of tube VIS is fed through coupling resistance 6| to the grid of tube V49 and produces an oppositc voltage on the anode oftube VIS. The negative feedback from the anode of tube V|9 through resistance 92 back to the grid of tube V?, is adjusted to provide unity gain for tube V| 9 and insure a balanced push-pull output. Condensers 5t, 93 and 34 operate in like manner to form a dynamic feedback path.

As was hereinabove mentioned, the multivibrator is of the kind having two positions lof stability. Once tripped, it continues in an operating position until restored. The restoration circuit |98 measures the sweep voltage |24 and, after a-predetermined level which is adjusted 4to insure the optimum length of the sweep has been reached, supplies the necessary restoring pulse to the gating circuit |04 which cuts of the sweeping portion of the cycle and restores the sweep voltage to its quiescent value. Tube V2il is ordinarily non-conducting, being biased past cut-off. However, the cathode thereof is connected through resistance 55 to one terminal of the sweep condenser e0. As condenser lill discharges during the sweeping portion of the cycle, the voltage on the cathode of tube V2U decreases and eventually tube V29 conducts. The point at which it starts to conduct determines the end of the sweeping portion and is adjusted by means of the bias on the grid of V29. This bias may be changed by varying the tap on potentiometer' El. When tube V29 begins to conduct, a negative pulse is generated at the anode thereof which is transmitted through resistance l2, gas tube V2I, and resistance I to the grid of the tube V6. Gas tube V2I serves to drop the high plate voltage of tube V to a value suitable for use on the grid of tube V6. The negative pulse thus supplied to the grid of the tube VS initiates the action which restores the multivibrator to its non-operating position in the manner already discussed. As the gating circuit It is restored to its non-operating position, the anode of tube V6 receives a positive pulse which is transmitted as hitherto described to the grid of the switching tube VI I which is thereby rendered conducting and recharges sweep condenser M. This change in the plate voltage of tube Val is also transmitted through the fast lock-out circuit lill and removes the negative pulse on the suppressor grid of the tube V4 which has kept the synchronizing amplifier inoperative to insure that no further tripping pulses would pass to affect the multivibrator.

Since the restoration of the sweep condenser to its normal or quiescent voltage takes a finite time, for the greatest precision it is necessary to protect the multivibrator from retripping until the sweep condenser is fully restored. In accordance with the invention, this is done by the slow lock-out circuit ille. The sweep voltage |24 is measured by the action of tube VIG. The grid of tube VIS is biased close to cut-off. As the sweep condenser 4S begins to discharge, marking the start of the sweep cycle, the negative change thereacross is transmitted through the tap on resistance i3 to the grid of the tube VIe, cutting it off. This causes a positive change on the anode of tube VIS which is transmitted through resistance lt, through the cathode follower VI3, gas tube VM, resistance BI and blocking diode V24 to the grid of the tube V23. Tube V23 amplies and reverses this pulse. This negative pulse is then supplied to the suppressor grid of the tube V4 and keeps the synchronizing amplifier cut olf. The pulse is also used to trip a single position multivibrator which is formed by tubes V23 and V26 and is adapted to keep the tube V4 cut off for an additional interval, determined by the variable condenser 93, after the negative pulse has been removed. The negative pulse is maintained on the suppresor grid as long as the tube VIG is cut off, which is as long as the voltage across the sweep condenser differs nieasurably from its normal quiescent value.

Another feature of the invention is the irnprovement which results in the faster restoration of the sweep condenser to its quiescent value, after the sweeping portion of the cycle has been completed. As was hereinabove discussed, during the sweeping portion the switching tube VII is cut oi. Also, after the sweep begins, the tube V16 is cut oif. As a result thereof, the anode voltage of tube VIS rises to its maximum positive value. Since the anode thereof is connected to the grid of the cathode follower VI3, the cathode voltage of tube VI3, which is supplied directly as the screen voltage of the tube VI I, is also at a maximum. Hence, during the sweeping portion,

the screen voltage thereof is at its maximum.

Since tube VII is then biased beyound cut-off, no screen current is drawn despite the high screen grid potential so that it is safe to operate at screen voltages higher than ordinarily permissible consistent with long tube life and reliable operation. When the positive pulse is received on the grid of the tube VII ending the sweeping portion of the cycle and commencing the return to the quiescent state, the high screen voltage present at that time insures the maximum plate current. The higher the plate current, the less is the restoration time. More concisely, the high screen voltage minimizes the resistance of tube VII which is in series with the charging circuit of the sweep condenser 40. The lower the series resistance, the faster the charging of the condenser 40.

This same feedback circuit to the screen grid of tube VII also serves to stabilize the zero spot on the cathode-ray tube screen which is another feature of the invention. The zero position on the tube screen is determined by the steady anode voltages of tubes VI8 and VIS since the anodes thereof are connected directly to the defiecting plates at terminals 98 and 99. |These, in turn, are determined by the voltages on the grids of tubes VI8 and VIS which are equal to that on the anode of tube VII. Since the sweep speed is varied by adjusting the sweep resistance 30, which is part of the plate load resistance of the tube VI I, any variation thereof tends to change the plate voltage. Since the zero spot is very sensitive to changes in the plate voltage of tube VI I, it is necessary to stabilize this voltage against fluctuations caused by variations in the plate load. Otherwise. it would become necessary to readjust the zero spot each time the sweep speed was changed, which would be a source of much inconvenience. For the purpose of illustration, suppose that the sweep resistance 30 is reduced tending to cause an increase in the plate voltage of tube VII. This is transferred to the grid of the tube VI8 and decreases the plate voltage thereof. This negative pulse is fed through the cathode follower VI1 and the voltage divider consisting of resistances 42, 43 and irl to the grid of tube VIS. This change is amplified, reversed in phase, and applied through the cathode follower VI3 to the screen grid of tube VII. Thus, a positive change of voltage at the anode of the tube VII will cause an increase in the screen grid voltage thereof. This effects a decrease in the tube impedance. The latter effect tends to restore the plate voltage to its original value. More concisely, resistance 3G and the impedance of tube VI I form a voltage divider which is tapped to supply the grid voltage of the tube VI8. As the resistance 3i] is decreased, the tube impedance must be decreased to maintain the voltage at the tap constant. This is done by a feedback circuit which varies the tube impedance in the same direction as the load is changed. This technique may be used apart from sweep circuits as a voltage-divider stabilizing circuit.

It is to be understood that the above-described arrangements are illustrative of the principles of the invention. Numerous other arrangements `may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What is claimed is:

i. A circuit for producing sweep voltages each cycle of which includes a sweeping portion followed in turn by a return portion and a quiescent portion during which the sweep voltage has a substantially constant value, comprising means for receiving synchronizing signals, an amplifier for said synchronizing signals, means connected to said amplifier for producing step voltages, each of which has an abrupt forward part, means initiated by said forward part of each step voltage for producing the sweeping portion of a sweep voltage cycle, means rendered active when a predetermined point on said sweeping portion of the sweep voltage has been reached for terminating the step voltage and in turn said sweeping portion of the sweep voltage, means initiated by the termination of said step voltage for causing said sweep voltage to return abruptly to its quiescent state, and means for rendering inactive the synchronizing amplifier on the occurrence of the forward part of said step voltage and for maintaining it inactive for a predetermined time after the sweep voltage has been returned to its quiescent state.

2. A circuit for producing sweep voltages according to claim 1, and characterized in that the amplifier for the synchronizing signal includes a control element, and further characterized in that the means for rendering inactive the synchronizing amplifier on the occurrence of the forward part of the step voltage includes means for returning a portion of said step voltage to said control element and the means for maintaining the amplier inactive for a predetermined time after the sweep voltage has been returned to its quiescent state includes means for returning a portion of said sweep voltage to the control element.

3c A sweep circuit according to claim 1 characterized in that the means initiated by the termination of the step voltage for causing the sweep voltage to return abruptly to its quiescent state includes an electron discharge device having a cathode, a control grid, a plate and a screen grid element, means for raising the screen grid potential during the sweeping portion of the sweep voltage, and means for reducing it during the return portion, whereby this return interval is minimized.

4. A sweep circuit comprising a space current device having a cathode, a control grid, a screen grid, and a plate element, means connected to said space current device for rendering it nonconducting, means in series with the plate element for producing the sweeping portion of a sweep voltage cycle as said space current device is rendered non-conducting and in turn for raising the potential on the screen grid element, means rendered active for making the space current device conducting after the sweep voltage has progressed for a predetermined interval, and means for reducing the screen grid potential as the space current device becomes conducting.

5. In a sweep circuit for use with a cathoderay tube, an arrangement for stabilizing the starting point of the sweep image on the cathoderay tube screen as the sweep speed is varied comprising a space current device having a plate,

a cathode, a first control element, and a second control element, a current path associated with said plate which includes a plate load resistance which is varied to change the sweep speed, means for using the plate voltage to X the starting point of the sweep image on the tube screen, and means for keeping the plate voltage constant as the plate load is varied, said means comprising a feedback circuit from the plate to the second control element.

6. A circuit for producing sweep voltages, each` cycle of which includes a sweeping portion followed in turn by a return portion and a quiescent portion, comprising means for producing a step voltage having an abrupt forward and an abrupt return part, a rst electron discharge device having a plurality of elements, including a cathode, a rst control element, a second control element and a. plate, a second electron discharge device having a plate, a cathode and a control element, a third electron discharge element having a plate, a cathode and a control element, means for supplying said step voltage to the cathode element of said rst electron device, a resistance in series with the plate of the first electron device, a condenser connected between the plate of the first electron device and the cathode of the third ele.,- tron device, means connecting the plate of the first electron device with the rst control element of the second electron device, means connecting the plate of the second electron device to the control element of the third, and means connecting the cathode of the third electron device to the second control element of the first electron device.

7. A circuit for producing sweep voltages according to claim 1 and characterized in that the sweep generator includes means for adjusting the rate of change of the sweeping portion of the sweep cycle, and means for keeping constant the quiescent portion of the sweep cycle as the sweep rate is varied.

8. A circuit for producing sweep voltages each cycle of which includes a sweeping portion followed in turn by a return portion and a quiescent portion during which the sweep voltage has a substantially constant value, comprising means for receiving synchronizing signals, means connected to said amplifier for producing step voltages, each of which has an abrupt forward part, means initiated by said forward part of each step voltage for producing the sweeping portion of a sweep voltage cycle, means for varying the rate of change of said sweeping portion, means rendered active when a predetermined point on said sweeping portion has been reached for terminating the step voltage and in turn said sweeping portion, means initiated by the termination of said step voltage for causing said sweep voltage to return abruptly to its quiescent, state, and means for keeping constant this quiescent state as the sweep rate of change is varied.

WILBUR L. GAINES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,075,966 Vance Apr. 6, 1937 2,171,614 Wendt Sept. 5, 1939 2,415,870 De Ryder Feb. 18, 1947 2,449,848 Hefele Sept. 21, 1948 .2,466,924 Bradford et al. Apr. 12, 1949 

